There is a conventional light fixture which is used after being attached to a power track arranged on a ceiling or the like. Such a light fixture includes a lamp and a down-transformer section serving as a device for lighting the lamp. However, since the size of the down-transformer section is not so small that the down-transformer section can be stored in the power track, the down-transformer section is stored in an outer envelope arranged independently of the lamp, and the down-transformer section is arranged under the power track. Therefore, the lamp and the outer envelope disadvantageously overhang under the power track in appearance. As a method of reducing the circuit of the down-transformer section to suppress the overhang of the outer envelope, the following two methods, i.e., a method of reducing the circuit of the down-transformer section and a method of devising a structure of a printed circuit board on which the electronic parts of the down-transformer section are mounted to reduce the down-transformer section in size are known.
In the two solving methods, a light fixture including the down-transformer section which is reduced in size to have preferable appearance when attached to the power track is proposed in JP11-111040A. However, this light fixture uses, as a lamp, an incandescent lamp lighted by the down-transformer section, a halogen lamp, or the like. On the other hand, a light fixture using a high-pressure discharge lamp such as an HID (High Intensity Discharged) lamp has a problem in which the circuit cannot be reduced much in size, since the number of parts is large due to a complex circuit configuration of the device for lighting the high-pressure discharge lamp (as described later) and temperatures of the electronic parts increase.
FIG. 28 shows a basic circuit of a conventional high-pressure discharge lamp lighting device. The device includes a rectifier circuit 92 containing a step-up chopper, a power control circuit 97 containing a step-down chopper, a polarity inversion circuit 93 containing a full bridge circuit, an high-pressure pulse generation circuit Ig, a control circuit 96 for performing drive control of a switching element Q95 for the step-up chopper, and a control circuit 98 for performing drive control for a switching element Q96 for the step-down chopper. Each circuit will be described below.
The rectifier circuit 92 includes a so-called step-up chopper circuit containing an inductor L93, a diode D95, a capacitor C95, and a switching element Q95 such as a MOSFET (Metal Oxide Silicon Field Effect Transistor) and a bridge rectifier DB. The bridge rectifier DB fully rectifies an AC voltage from a commercial AC power supply AC to generate a pulsating-flow voltage. The step-up chopper circuit converts the pulsating-flow voltage generated by the bridge rectifier DB into a DC voltage to output the DC voltage.
The power control circuit 97 contains the switching element Q96 such as a MOSFET turning on/off at several 10 KHz, a diode D96, an inductor L94, and a capacitor C96, an output current of which is of chopping-wave shape. A voltage depending on an output current output from the power control circuit 97 is induced at the secondary winding of the inductor L94. The induced voltage is input to the control circuit 98 through a series-connected resistor R94. The control circuit 98 performs zero-cross switching control of the switching element Q96 on the basis of the voltage input from the secondary winding of the inductor L94. The capacitor C96 is used to remove harmonic components from the output current of a primary winding of the inductor L94.
The polarity inversion circuit 93 converts a DC voltage from the power control circuit 97 into a rectangular wave AC voltage having a low frequency of several 100 Hz through a full-bridge circuit including switching elements Q91 to Q94 such as MOSFETs and supplies the rectangular wave AC voltage to a high-pressure discharge lamp DL.
The high-pressure pulse generation circuit Ig is for generating a high-pressure pulse to cause dielectric breakdown between the electrodes of the high-pressure discharge lamp DL, and is used to start the high-pressure discharge lamp DL. After the high-pressure discharge lamp DL is started, the operation of the high-pressure pulse generation circuit Ig is halted.
The light fixture including the high-pressure discharge lamp DL lighted by the lighting device is disclosed in JP14-75045A. It is desired that the circuit of the lighting device is changed to be smaller so as to reduce the light fixture in size.
On the other hand, as another solving method, a method of devising the structure of a printed circuit board on which electronic parts are mounted to reduce an electronic circuit module in size is proposed in JP5-327161A. This has a structure in which an auxiliary circuit board is arranged perpendicularly to a main circuit board. The auxiliary circuit board has one pair of substrate support sections projecting from both the longitudinal ends to the main circuit board side, and the main circuit board has fixing holes into which the substrate support sections of the auxiliary circuit board penetrate. When the auxiliary circuit board is mounted on the main circuit board, the substrate support sections are inserted into the fixing holes, so that the auxiliary circuit board can be held perpendicularly to the main circuit board. In this manner, the electronic parts to be mounted on the printed board can be three-dimensionally mounted on the main circuit board and the auxiliary circuit board, and therefore the electronic circuit module can be reduced in size.
However, in this mounting structure, a plurality of terminal pads aligned along the long side of the auxiliary circuit board and a plurality of pads aligned on the upper surface of the main circuit board are soldered on the parts surface side of the main circuit board. For this reason, for example, in case that the soldered surface of the main circuit board is dipped into a solder tank while the auxiliary circuit board is mounted on the parts surface of the main circuit board to solder the part leads of the main circuit board, the auxiliary circuit board cannot be connected to the main circuit board simultaneously with the parts. As a matter of course, even in this mounting structure, if all the parts on the main circuit board are mounted on the upper surface of the main circuit board simultaneously with the auxiliary circuit board, soldering of the parts on the main circuit board and soldering of the auxiliary circuit board and the main circuit board can be simultaneously performed.
However, as indicated in the reference, when the surface mounting is done, reflow soldering is performed, and thus heating by the reflow soldering causes another problem such as positioning errors of the parts mounted on the auxiliary circuit board. In order to prevent the positioning errors, another member which holds the parts on the auxiliary circuit board to prevent the positioning errors of the parts is required to increase the cost disadvantageously. The substrate support sections of the auxiliary circuit board are easily broken. If the substrate support sections are broken, all the substrates cannot be used. Furthermore, since the auxiliary circuit board is mounted on the upper surface (surface on which electronic parts are mounted) of the main circuit board, the terminal pads of the auxiliary circuit board are located above the upper surface of the main circuit board. Therefore, the electronics parts to be mounted on the auxiliary circuit board are mounted at positions which are above the terminal pads and which is distant from the upper surface of the main circuit board, so that the height of the projection of the auxiliary circuit board from the upper surface of the main circuit board is made difficult to be small. For this reason, the electronic circuit module on which the electronic parts cannot be easily downsized.
The present invention has been made in consideration of the above problems, and has as its object to provide a compact high-pressure discharge lamp lighting device and a light fixture equipped with the high-pressure discharge lamp lighting device.